One trick I've used is to get one of those copper or stainless steel 'pot scrubbers'. The sort of thing that's shaped about like a donut with a filled in hole.

If you nip a bit at the 'donut hole' part of the scrubber, you can get it to unravel into something that looks like a section of fishnet panty-hose.

Cut about a third of that away and set it aside. Open up the muffler end and stuff in the part that you've saved. You don't want to put too much in there because you want to avoid restricting the exhaust too much.